earth science

Tourmaline

Tourmaline is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Tourmaline rather than just read about it. In short: Tourmaline ( TOOR-mə-lin, -⁠leen) is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors.

Key takeaways

Tourmaline belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tourmaline to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tourmaline from memory before moving on to harder problems.

Reference excerpt

Tourmaline ( TOOR-mə-lin, -⁠leen) is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors. The name is derived from the Sinhalese tōramalli (ටෝරමල්ලි), which refers to the carnelian gemstones.

History Brightly colored Ceylonese gem tourmalines were brought to Europe in great quantities by the Dutch East India Company, to satisfy a demand for curiosities and gems. Tourmaline was sometimes called the "Ceylonese Magnet" because it could attract and then repel hot ashes due to its pyroelectric properties. Tourmalines were used by chemists in the 19th century to polarize light by shining rays onto a cut and polished surface of the gem.

Species and varieties Commonly encountered species and varieties of tourmaline include the following:

Schorl species Brownish-black to black—schorl Dravite species (from the Drave district of Carinthia) Dark yellow to brownish-black—dravite Elbaite species (named after the island of Elba, Italy) Red or pinkish-red—rubellite variety Light blue to bluish-green—indicolite variety (from indigo) Green—verdelite variety Colorless—achroite variety (from Ancient Greek άχρωμος (ákhrōmos) 'colorless')

Schorl

The most common species of tourmaline is schorl, the sodium iron (divalent) endmember of the group. It may account for 95% or more of all tourmaline in nature. The early history of the mineral schorl shows that the name "schorl" was in use prior to 1400 because a village known today as Zschorlau (in Saxony, Germany) was then named "Schorl" (or minor variants of this name), and the village had a nearby tin mine where, in addition to cassiterite, black tourmaline was found. The first description of schorl with the name "schürl" and its occurrence (various tin mines in the Ore Mountains) was written by Johannes Mathesius (1504–1565) in 1562 under the title "Sarepta oder Bergpostill". Up to about 1600, additional names used in the German language were "Schurel", "Schörle", and "Schurl". Beginning in the 18th century, the name Schörl was mainly used in the German-speaking area. In English, the names shorl and shirl were used in the 18th century. In the 19th century the names common schorl, schörl, schorl and iron tourmaline were the English words used for this mineral.

Dravite

Dravite, also called brown tourmaline, is the sodium magnesium rich tourmaline endmember. Uvite, in comparison, is a calcium magnesium tourmaline. Dravite forms multiple series, with other tourmaline members, including schorl and elbaite. The name dravite was used for the first time by Gustav Tschermak (1836–1927), Professor of Mineralogy and Petrography at the University of Vienna, in his book Lehrbuch der Mineralogie (published in 1884) for magnesium-rich (and sodium-rich) tourmaline from village Dobrova near Unterdrauburg in the Drava river area, Carinthia, Austro-Hungarian Empire. Today this tourmaline locality (type locality for dravite) at Dobrova (near Dravograd), is a part of the Republic of Slovenia. Tschermak gave this tourmaline the name dravite, for the Drava river area, which is the district along the Drava River (in German: Drau, in Latin: Drave) in Austria and Slovenia. The chemical composition which was given by Tschermak in 1884 for this dravite approximately corresponds to the formula NaMg3(Al,Mg)6B3Si6O27(OH), which is in good agreement (except for the OH content) with the endmember formula of dravite as known today. Dravite varieties include the deep green chromium dravite and the vanadium dravite.

Elbaite

A lithium-tourmaline elbaite was one of three pegmatitic minerals from Utö, Sweden, in which the new alkali element lithium (Li) was determined in 1818 by Johan August Arfwedson for the first time. Elba Island, Italy, was one of the first localities where colored and colorless Li-tourmalines were extensively chemically analysed. In 1850, Karl Friedrich August Rammelsberg described fluorine (F) in tourmaline for the first time. In 1870, he proved that all varieties of tourmaline contain chemically bound water. In 1889, Scharitzer proposed the substitution of (OH) by F in red Li-tourmaline from Sušice, Czech Republic. In 1914, Vladimir Vernadsky proposed the name Elbait for lithium-, sodium-, and aluminum-rich tourmaline from Elba Island, Italy, with the simplified formula (Li,Na)HAl6B2Si4O21. Most likely the type material for elbaite was found at Fonte del Prete, San Piero in Campo, Campo nell'Elba, Elba Island, Province of Livorno, Tuscany, Italy. In 1933 Winchell published an updated formula for elbaite, H8Na2Li3Al3B6Al12Si12O62, which is commonly used to date written as Na(Li1.5Al1.5)Al6(BO3)3[Si6O18](OH)3(OH). The first crystal structure determination of a Li-rich tourmaline was published in 1972 by Donnay and Barton, performed on a pink elbaite from San Diego County, California, United States.

Chemical composition

The tourmaline mineral group is chemically one of the most complicated groups of silicate minerals. Its composition varies widely because of isomorphous replacement (solid solution), and its general formula can be written as XY3Z6(T6O18)(BO3)3V3W, where:

X = Ca, Na, K, ▢ = vacancy Y = Li, Mg, Fe2+, Mn2+, Zn, Al, Cr3+, V3+, Fe3+, Ti4+, ▢ = vacancy Z = Mg, Al, Fe3+, Cr3+, V3+ T = Si, Al, B B = B, ▢ = vacancy V = OH, O W = OH, F, O

Mineral species that were named before the IMA was founded in 1958 do not have an IMA number. The IMA commission on new mineral names published a list of approved symbols for each mineral species in 2021. A revised nomenclature for the tourmaline group was published in 2011.

Physical properties

Crystal structure

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Tourmaline

Start with the simplest possible case. Write down what Tourmaline claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tourmaline before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tourmaline ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tourmaline

In research: Tourmaline appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tourmaline in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tourmaline is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aluminium minerals, Cyclosilicates, Gemstones, so understanding it makes those chapters shorter.
In everyday life: Look for Tourmaline outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Tourmaline in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tourmaline means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tourmaline out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tourmaline in simple terms?

Why does Tourmaline matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tourmaline?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tourmaline.